A Digital Rights Management (DRM) refers to a system technology for safely protecting rights for digital contents and systematically managing them. The DRM provides a protecting and managing scheme for preventing the illegal copy of a content, acquiring DRM contents RO, and contents generating, contents transferring and contents processing.
FIG. 1 illustrates a construction of a DRM system. The DRM system controls content issued to a user by a content provider to be used only in a right-limit of RO. Here, the content provider refers to an entity corresponding to a Content Issuer (CI) and/or a Rights Issuer (RI).
The CI issues a protected content using a particular encryption key so as to protect the content from users having no access right therefor, while the RI issues RO required to use the protected content.
A DRM agent is mounted in a device (or terminal) thus to receive the protected content and its RO. The DRM agent then analyzes ‘permission’ (license) included in the RO and thus changes the protected content into a usable format in the corresponding terminal, thereby controlling the use of the content.
On the other hand, the DRM technology proposes a method by which a specific group of devices (terminals) which is so-called user domain can only use digital contents (i.e., DRM contents).
Here, the user domain (or domain) denotes a collection of user devices. Devices belonging (subscribed or joined) to the user domain denote domain members, each of which shares a common domain key. The domain key is used to decode a domain Rights Object (so-called domain RO). The domain RO is a type of RO shared by devices within the domain.
However, in the user domain related DRM technology, nothing has been provided to solve a technical problem as to how to manage specific devices which intend to join or leave the user domain, namely, DRM agents mounted in the devices. In addition, in view of the user domain management, it is required to solve a problem as to how to provide domain keys to specific DRM agents subscribed (joined) to the user domain in the DRM system.